If the burning isn't consistent, it's probably not NGU or another STD.
You also didn't have any wbc in your urine, which is how NGU is diagnosed.
How's your water intake? Do you drink a lot of alcohol or caffeine? Juices? Try drinking more water and less of the other stuff - especially lay off the alcohol and caffeine as those are really dehydrating - and see how you feel. Even if you aren't dehydrated, alcohol, caffeine, sodas and juices can irritate the bladder, causing burning when you pee.
Of course, it could definitely be in your head, too. It's always best to rule out a physical cause first, though, so try more water and less of the rest and see how you feel.
I don't know why you are so anxious about this, if guilt is involved or something, but remember that guilt doesn't equal risk, and exposure doesn't equal transmission.